We are investigating the nueronal basis of reproductive behavior in the marine mollusk, Aplysia. As part of this investigation peptides from the atrial gland, located in the reproductive track, have been chemically purified. They are being used in behavioral and physiological experiments to determine their possible roles as pheromones and/or chemical stimuli that are important for understanding the behavior. Mass spectrometry will be used to identify known polypeptides and uncover new ones for further chemical characterization.